1. Field of the Invention
The present application relates to sheet feeding apparatus used to supply sheets of paper in image reading or recording apparatus. More particularly, the present application provides a sheet feeding apparatus having an improved sheet pick-up mechanism.
2. Description of the Related Art
Conventional sheet feeding apparatus typically use a sheet pick-up device for picking up sheets of paper from a paper delivery tray and a sheet transfer device for transferring the sheets to an image reader. Some pick-up devices use a cam that rotates to engage a sheet of paper from the bottom of the delivery tray and position an edge of the sheet onto rollers which transfer the sheet to the image reader. In order to ensure that the next sheet of paper is properly picked-up and transferred to the image reader, the sheet feeding apparatus has to know the position of the cam prior to picking-up the sheet. This is achieved by moving the cam to a predefined home position prior to picking-up the sheet. However, the rotational speed of the cam is typically slower than the rotational speed of the rollers so that when the rollers grab the sheet the cam must release the sheet so that: 1) the cam does not retard the speed at which the sheet is fed to the image reader; and 2) the cam is not damaged by the acceleration force created by the rollers. One attempt to avoid these problems is to connect the cam to a clutch so that when the rollers grab the sheet the clutch actuates causing the cam to release the sheet.
Once the clutch actuates to cause the cam to release the sheet, the actual position of the cam is unknown. Thus, to determine the location of the cam, conventional sheet feeding apparatus add sensors and additional structure to the pick-up device to determine the location of the cam.
For example, Japanese Laid-open Publication No. 05-162888, appears to discuss a pick-up device that returns and stops at a home position using a combined cam and spring board mechanism. As a result, the cost of manufacturing such a pick-up device increases the cost of manufacturing the sheet feeding apparatus.